Differences in structure of the dough. In the chapter on batters
and doughs it was found that differences in structure of batters and doughs
were due to several causes, i.e., the method of mixing or combining of
ingredients, the temperature of the ingredients when mixed, the extent
of mixing, the plasticity of the fat used, the ingredients used, and the
proportions of these ingredients. It is rather diflficult to exactly duplicate
the structure of a dough, but it is particularly difficult when the material
is thin like pastry. The fat or oil is seldom distributed evenly throughout
the dough. This gives structural weakness in certain areas. For this reason
breaking tests of individual pastries may vary considerably.
Theory concerning differences of shortening power of dif-
ferent fats and oils. The theory for differences in shortening power
of different fats and oils is based upon the concepts of differences in
cohesion, adhesion, adsorption at interfaces, and orientation of molecules.
These are in turn based on the concept of polarity. Polar groups or polar
molecules, owing to an electric charge, are very reactive and strongly
attracted to each other. Some substances like fatty acids have polar groups,
while a portion of the molecule is non-polar. This theory for the shorten-
UNSATURATED FATTY ACIDS 563
ing power of fats and oils has been developed from the work of Lang-
muir, Harkins, and their co-workers, upon cohesion, adhesion, interfacial
tension, and molecular attraction, between water and organic liquids.
Langmuir has reported : ''When a small quantity of an oil, such as
olive oil, is placed upon a large clean surface of water, the oil spreads
rapidly upon the water surface until a definite area has been covered, and
then the oil shows little or no tendency to spread further." The following
is a brief summary of his article. Some portions of the molecule have greater
affinity for water than other parts. In determining the cause of this spread-
ing of the oil upon the water he found that the film was one molecule
thick. If the cause of spreading is an attraction between the oil and water
this attraction may be the molecule as a whole or certain portions of the
molecule may have greater attraction than other parts for the water. If
the whole molecule is attracted there would be solubility of oil in water.
If a portion of the oil molecule is attracted by the water while another
portion is more attracted by the oil molecules we have a ready explana-
tion of the spreading of the oil on the water.
If oleic acid is considered, as an example, the carboxyl group has a
strong affinity for water, and when placed on water this group is probably
absorbed in it. The hydrocarbon chain of oleic acid has no attraction for
water but it is attracted by other hydrocarbon chains. From this, one can
picture the hydrocarbon chains as standing in the air side by side and the
carboxyl group dissolved in the water. Since the hydrocarbon chains have
an attraction for each other when the amount of oleic acid upon the
surface of the water is small, there is a tendency for it to remain in a
globule. This attraction of parts of the molecule for each other is in the
nature of a chemical force. With very small amounts of oleic acid the
hydrocarbon chain may lie along the surface of the water. With enough
for a layer the chains may stand upright.
Page 448
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Differences in structure of the dough. In the chapter on batters
and doughs it was found that differences in structure of batters and doughs
were due to several causes, i.e., the method of mixing or combining of
ingredients, the temperature of the ingredients when mixed, the extent
of mixing, the plasticity of the fat used, the ingredients used, and the
proportions of these ingredients. It is rather diflficult to exactly duplicate
the structure of a dough, but it is particularly difficult when the material
is thin like pastry. The fat or oil is seldom distributed evenly throughout
the dough. This gives structural weakness in certain areas. For this reason
breaking tests of individual pastries may vary considerably.
Theory concerning differences of shortening power of dif-
ferent fats and oils. The theory for differences in shortening power
of different fats and oils is based upon the concepts of differences in
cohesion, adhesion, adsorption at interfaces, and orientation of molecules.
These are in turn based on the concept of polarity. Polar groups or polar
molecules, owing to an electric charge, are very reactive and strongly
attracted to each other. Some substances like fatty acids have polar groups,
while a portion of the molecule is non-polar. This theory for the shorten-
UNSATURATED FATTY ACIDS 563
ing power of fats and oils has been developed from the work of Lang-
muir, Harkins, and their co-workers, upon cohesion, adhesion, interfacial
tension, and molecular attraction, between water and organic liquids.
Langmuir has reported : ''When a small quantity of an oil, such as
olive oil, is placed upon a large clean surface of water, the oil spreads
rapidly upon the water surface until a definite area has been covered, and
then the oil shows little or no tendency to spread further." The following
is a brief summary of his article. Some portions of the molecule have greater
affinity for water than other parts. In determining the cause of this spread-
ing of the oil upon the water he found that the film was one molecule
thick. If the cause of spreading is an attraction between the oil and water
this attraction may be the molecule as a whole or certain portions of the
molecule may have greater attraction than other parts for the water. If
the whole molecule is attracted there would be solubility of oil in water.
If a portion of the oil molecule is attracted by the water while another
portion is more attracted by the oil molecules we have a ready explana-
tion of the spreading of the oil on the water.
If oleic acid is considered, as an example, the carboxyl group has a
strong affinity for water, and when placed on water this group is probably
absorbed in it. The hydrocarbon chain of oleic acid has no attraction for
water but it is attracted by other hydrocarbon chains. From this, one can
picture the hydrocarbon chains as standing in the air side by side and the
carboxyl group dissolved in the water. Since the hydrocarbon chains have
an attraction for each other when the amount of oleic acid upon the
surface of the water is small, there is a tendency for it to remain in a
globule. This attraction of parts of the molecule for each other is in the
nature of a chemical force. With very small amounts of oleic acid the
hydrocarbon chain may lie along the surface of the water. With enough
for a layer the chains may stand upright.